"Intrinsic angular momentum"

[Butch]

Taken alone I understand each of these words... 

I am at a loss as to spin and why it is referred to as intrinsic angular momentum, it is not motion, not torque, not spin... Obviously it is intrinsic... Please help, I have been reading all kinds of texts and I still just don't get it.

Edited February 28, 2018 by Butch

[Strange]

Because particles have zero size, there is no way it can be described in terms of classical rotation. So it is just a property they have, like mass or charge. 

[Butch]

4 minutes ago, Strange said:

Because particles have zero size, there is no way it can be described in terms of classical rotation. So it is just a property they have, like mass or charge. 

I can describe the "size" of a particle by its mass or charge... Spin is different, it is not linear.

I can apply Coulomb's law to charge, I can apply Newton's law to mass... I can even feel them physically. Perhaps you could provide a link? Maybe the history?

Thank you, Strange.

[Strange]

6 minutes ago, Butch said:

I can describe the "size" of a particle by its mass or charge... Spin is different, it is not linear.

These are not size. Size is measured in metres. 

In what way are mass and charge “linear”, and why is it relevant. 

[Butch]

1 minute ago, Strange said:

These are not size. Size is measured in metres. 

In what way are mass and charge “linear”, and why is it relevant. 

Size is magnitude, I get it particles have no dimension... Still lost on spin, I could go on and study quark interaction, but I really want to understand spin first, not just accept and move on.

[Strange]

3 minutes ago, Butch said:

Still lost on spin

It is just a property that particles have. It has units of angular momentum. 

You could look up Pauli if you need the history. 

[Butch]

18 minutes ago, Strange said:

It is just a property that particles have. It has units of angular momentum. 

You could look up Pauli if you need the history. 

Thanks, I will try that, I am familiar with the principle... I guess what I really need to find is the classical physical evidence for spin.

[Strange]

It was, from memory, a couple of things. Pauli proposed an (unknown) property that would distinguish pairs of electrons in order to explain observed spectral lines. Then it was suggested that particles must have angular momentum because of conservation laws. It was then realised that (quantised) angular momentum would be the property required by Pauli. 

The Stern-Gerlach experiment showed that angular momentum was quantised. 

[StringJunky]

Charges are created by spinning objects. Electrons have charge but they can't spin fast enough i.e faster than the speed of light, for their size to generate the degree of magnetic moment that they do... it's much bigger than is allowed for their size but it's there as a fact. The consequence of this is that they  have to call it intrinsic angular moment because it's there, even though they can't fully explain how it does  it. The 'spin' is an integral part as much as the mass of the particle. I might need correcting on this but I think it  has to have spin because it has charge.

50 minutes ago, Butch said:

Thanks, I will try that, I am familiar with the principle... I guess what I really need to find is the classical physical evidence for spin.

 

Edited March 1, 2018 by StringJunky

[Strange]

4 minutes ago, StringJunky said:

Charges are created by spinning objects

I don’t think that is correct. Photons have spin but no charge. 

[StringJunky]

3 minutes ago, Strange said:

I don’t think that is correct. Photons have spin but no charge. 

 I'm talking about a physical spin there,  not quantum spin.

[Butch]

On 2/28/2018 at 5:49 PM, Strange said:

It is just a property that particles have. It has units of angular momentum. 

You could look up Pauli if you need the history. 

Thanks, I will try that, I am familiar with the principle... I guess what I really need to find is the classical physical evidence for spin.

Ok, particles have magnetic fields, we quantized this as angular momentum...

Correct?

[JohnMnemonic]

Quote

Charges are created by spinning objects. Electrons have charge but they can't spin fast enough i.e faster than the speed of light, for their size to generate the degree of magnetic moment that they do... it's much bigger than is allowed for their size but it's there as a fact. The consequence of this is that they  have to call it intrinsicangular moment because it's there, even though they can't fully explain how it does  it. The 'spin' is an integral part as much as the mass of the particle.

Problem is, that you can't think about electrons as about physical objects - they exist as probability distribution and there are no mechanical forces, connected with them. Electron has no specific location, spin or momentum (until it's measured)

Quote

I might need correcting on this but I think it  has to have spin because it has charge.

Neutron has spin (magnetic moment), while it doesn't have charge...

[Strange]

15 hours ago, Butch said:

I guess what I really need to find is the classical physical evidence for spin.

Stern-Gerlach?

But there isn't really any "classical" evidence, because it is a quantum effect, so I'm not sure what you are looking for.

[Butch]

9 hours ago, Strange said:

Stern-Gerlach?

But there isn't really any "classical" evidence, because it is a quantum effect, so I'm not sure what you are looking for.

The magnetic property is enough... Stern Gerlach demonstrates this just fine, if the electron has no dimension, then it does have a property equivalent to angular momentum... Somewhat akin to the relationship of acceleration and gravity.

Edited March 3, 2018 by Butch

[Strange]

3 minutes ago, Butch said:

The magnetic property is enough...

https://en.wikipedia.org/wiki/Electron_magnetic_moment

[Butch]

1 minute ago, Strange said:

https://en.wikipedia.org/wiki/Electron_magnetic_moment

Thx, btw we cross posted... 

[swansont]

On 2/28/2018 at 7:16 PM, StringJunky said:

 I'm talking about a physical spin there,  not quantum spin.

Charge is not created by spinning an object.

[Eise]

On 28.2.2018 at 11:49 PM, Strange said:

You could look up Pauli if you need the history. 

Or Dirac. AFAIK spin (and antimatter) rolled out of his theoretical synthesis of QM and special relativity.

[StringJunky]

42 minutes ago, swansont said:

Charge is not created by spinning an object.

Am  I conflating charge with magnetic moment; it's moving charge that creates it? I've forgotten what I was thinking at the time now. 

Edited March 4, 2018 by StringJunky

[swansont]

1 hour ago, StringJunky said:

Am  I conflating charge with magnetic moment; it's moving charge that creates it? I've forgotten what I was thinking at the time now. 

That could be. Classically, you need a moving charge to create a magnetic field. Rotation or revolution would create a magnetic moment. QM requires angular momentum and charge.

[StringJunky]

10 minutes ago, swansont said:

That could be. Classically, you need a moving charge to create a magnetic field. Rotation or revolution would create a magnetic moment. QM requires angular momentum and charge.

Yeah. Cheers. Charge is an intrinsic property. 

[Butch]

4 hours ago, swansont said:

That could be. Classically, you need a moving charge to create a magnetic field. Rotation or revolution would create a magnetic moment. QM requires angular momentum and charge.

Hmm... Wouldn't a dipole present a planar field perpendicular to charge?

Ah, classically...  Understood.

Edited March 4, 2018 by Butch

[swansont]

13 hours ago, Butch said:

Hmm... Wouldn't a dipole present a planar field perpendicular to charge?

Ah, classically...  Understood.

A dipole would present a dipole field.  

[Butch]

3 hours ago, swansont said:

A dipole would present a dipole field.  

Of course, silly me! However why classically a moving charge, isn't that relative?

Edited March 5, 2018 by Butch